内蒙古苏左旗地区古生代两类花岗岩类的基本特征和构造意义

The Main Characteristics and Tectonic Implications of Two Kinds of Paleozoic Granitoids in Sunidzuqi, Central Inner Mongolia

内蒙古苏左旗地区古生代造山带中的花岗岩可分成两个序列，即白音宝力道序列和巴颜哈拉图序列。前者主要由角闪闪长岩、石英闪长岩、英云闪长岩及花岗闪长岩等同源岩石组成，化学成分以富ＦｅＯ、ＭｇＯ、Ｎａ２Ｏ、Ｃｏ、Ｎｉ、Ｓｒ和贫ＳｉＯ２、Ｋ２Ｏ、Ｒｂ为特征，稀土分布型式为平坦型，负铕异常不明显，单颗粒锆石Ｕ－Ｐｂ同位素年龄为４１４～４１８Ｍａ。后者主要由花岗闪长岩、二长花岗岩和钾长花岗岩组成，化学成分以富ＳｉＯ２、Ｋ２Ｏ、Ｒｂ和贫ＣａＯ、ＦｅＯ、ＭｇＯ、Ｃｏ、Ｓｒ为特征，轻重稀土较强分馏，负铕异常明显，单颗粒锆石Ｕ－Ｐｂ同位素年龄为３６３Ｍａ。两个序列花岗岩在空间上密切共生，均呈近东西向带状分布，并平行于其南侧的早古生代蛇绿混杂带和高压蓝片岩带。白音宝力道序列属于岛弧型花岗岩类（Ｉ型），巴颜哈拉图序列属于碰撞型花岗岩类（Ｓ型）。

The granitoids occured in Paleozoic orogenic belts of Sunidzuqi, Central Inner Mongolia, can be divided into two rock suits. They are Beinbaolidao suits composed of hornblende diorite, quartz diorite, tonalite and granodiorite, and Bainhalatu suits which include biotite granodiorite, biotite granite and two mica high K granite. The Beinbaolidao suits have relatively flat REE models, a slightly negative Eu abnormality and a zircon U Pb age of 414￣418Ma, and are characterized of high FeO, MgO, Na 2O, Co, Ni, Cr and low SiO 2, K 2O, Rb. The Bainhalatu suits, however, have strong contrast between LREE and HREE, an important negative Eu abnormality and a single zircon U Pb age of 363Ma, and are typical of high SiO 2, K 2O, Rb and low CaO, FeO, MgO, Co, Sr. The two rock suits are approximately EW trending and parallel with the early Paleozoic high P blueschist belt and ophiolitic melange, just south of the granitoid zones. They have significant disparities in petrology and geochemistry, which indicate that they come from completely different source regions and have different petrogenesis. Our research suggests that Beinbaolidao Suits belong to island arc granitoids (I type), and Bainhalatu suits to syn collisional granitoids (S type). They were produced during processes of Paleozoic subduction and collision between the North China plate and the South Mongolia plate, respectively.